The residence time or lifetime of atmospheric water vapour conveys the time and distance travelled between evaporation and subsequent precipitation. But how it responds to different climate drivers is not well understood, feeding into climate model uncertainty in hydroclimate change.
Øivind Hodnebrog of the CICERO Center for International Climate Research, Norway, and co-authors in Europe, the United States and Japan study this through climate models. They isolate the response of water vapour to greenhouse gases (carbon dioxide, methane), aerosols (black carbon, sulfate) and solar radiation. They also compare the fast response — the immediate adjustment of water vapour to the presence of a climate driver — with the slow response after surface temperature equilibrates. Water vapour lifetime increased by about 25% in a high-emissions scenario, and black carbon showed the highest impact, particularly in the fast response. These results highlight the role that black carbon emissions can play in the hydrological cycle and give insight into future water vapour lifetimes and the associated circulation cells that transport moisture from source to sink.
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Langenbrunner, B. Long live water vapour. Nat. Clim. Chang. 9, 906 (2019). https://doi.org/10.1038/s41558-019-0653-z